1. Field of the Invention
The invention pertains to the field of chain tensioners or guides. More particularly, the invention pertains to a two-shot unified chain tensioner arm or guide.
2. Description of Related Art
Chain tensioner arms and guides are known to be used in internal combustion engines. In a typical engine with one or more overhead camshafts because the distance from the camshaft to the crankshaft is increased, it is essential to incorporate in the timing chain system guiding and tensioning elements so as to ensure that chain tension is maintained within acceptable limits.
Because these guiding elements are in continuous contact with the moving chain, the elements need wear-resistance and have frictional characteristics. They cause neither degradation of the contact surfaces nor timing drive system inefficiencies. Additionally because in some instances the contact forces between the chain and the guide or tensioner arm can be substantial, they must possess substantial structural strength so as to withstand these contact forces.
Typically one of the contact element material solutions involves using a nylon 6/6 type surface because of its superior friction, wear, and high temperature characteristics. However this form of material does not have the structural integrity to handle forces transmitted from the chain to the guiding system components or the forces applied from the tensioner arm to the chain. A common solution to this issue is to have a metallic or fiber reinforced plastic structural member—cast iron, die-cast aluminum, glass filled nylon or stamped steel—for supporting the nylon contact surface. This method requires then to either assemble the structure or wear surface into a final part. Alternatively, the method requires completely finishing the structure element and then inserting it in a mold and thereby producing the contact surface on top of the structure element. In either case the dissimilarity of the materials results in some unique problems that are difficult to overcome because of the assembly process and dissimilar expansion characteristics of the material involved. In addition, the cost of these non-unified assemblies is relatively high.
With regard to assembly issues, it is noted that not only the tolerances of the mating elements must be carefully considered, but also the structural integrity of the interface must be maintained both at room temperature and at elevated engine operating temperatures. Additionally because the materials are dissimilar, their expansion and contraction characteristics will differ, thereby at temperature extremes, special stresses may occur due to physical constraints. Alternatively, because the interfaces between the materials are physically altered due to the occurrence that one of the elements may have expanded or contracted by an amount greater than its mating counterpart.
U.S. Pat. No. 4,832,664 teaches a guide rail, and method of making same, for the guiding and/or tightening of chains that are used in internal-combustion engines, for example, for driving camshafts, auxiliaries or the like is disclosed. For reasons concerning weight and manufacturing, the guide rail consists of a plastic material and is formed by a slideway lining body and a carrier. Both the carrier and the slideway lining body are produced in a progressive manufacturing cycle and are interconnected via one or several dovetailed connections.
However, the above guide rail, and method of making same requires two separate steps of molding. The method requires the need to remove the carrier parts from the mold after a first step. Then in a separate step, the slideway lining s molded over the carrier. Having the two separate steps has its disadvantages. They include: two separate devices for forming each piece such as two separate molding devices, or at least the need to remove the parts from the mold after the first step is required; and lastly significant outlay of cost and space for making the tensioner arm or the guide.
Therefore, there is a need to combine the two steps using the same basic molding equipment using a special mold which can produce the final product without the need to remove the parts from the mold after the first step.